There is no such thing as a stupid question. Well other than how do I get a ukara licence.
To answer your question most grenade launchers are actually like oversized shotguns. You load them with gas and some bbs and they shower out when fired.
ICs has made a new type that includes explode on impact, smoke and timed projectiles however they are unlikely to be allowed in the UK. The Russians are their main market and basically anywhere else with very relaxed H+S regulations.
There are mortars used by various sites and Tlsfx (? Close enough) sell one that fires pyro but use will probably be limited at most sites.
Some people make something along the howitzer/artillary lines by using compressed gas or an over sized spud gun ( YouTube is your friend they aren't that hard to make) and fire anything from tennis balls to nerf footballs that give a nice whistle as they drop towards you.
I hope that clears up your question